This invention relates to new and useful improvements in the remote control of fluid flow utilizing a valve incorporating an automatic time delay.
In certain industrial applications, it is beneficial to have control over a distant fluid flow in such a way that some predictable delay is incorporated automatically between the actuating means and the function being controlled.
Although the present description and drawings relate to oil well drilling, nevertheless the device can be used in other industrial applications.
In the drilling of petroleum exploratory wells, it is desirable to control and therefore prohibit, the passage of natural gas from the downhole drilling bit location to the earth's surface through the borehole annulus and also through the hollow drill stem itself.
Such control is mandatory for the prevention of costly "blowouts" that may occur in the process of drilling wells for the recovery of petroleum products.
Conventionally, control of gas flow through the bore-hole annulus is by means of "blowout preventers" installed at the surface and some control is exercised over the passage of gas through the interior of the drill stem by means of a downhole "float valve" and the present invention relates primarily to improvements in downhole "float valve" assemblies.
The present downhole float valve assemblies often cause what is known as "hydraulic sticking" of the drill string. As the drill string is lowered into the borehole subsequent to bit changing or the like, the lower members of the drill string (the drill collars) often become coated with various matter (e.g. cuttings and/or mudcake) suspended in the drilling fluid and when the interior of the drill string is subjected to the drilling fluid pressure imposed by the surface pumps, the drilling fluid itself causes the downhole float valve to open thereby permitting the passage of drilling fluid down through the drill bit and into the borehole annulus where it normally would proceed back to the surface.
However, the material in suspension in the annulus fluid sometimes becomes compressed upwardly as a result of the surface pump pressure thus causing a complete or partial blocking of the annulus route intended for the return of the drilling fluid to the surface.
The continuing application of pressure by the surface pumps therefore causes a downhole force imbalance in such a direction as to cause the float valve to close thereby leaving a section of the downhole annulus, pressurized, resulting in a hydraulically "stuck" situation.
In float valve applications, the present state of the art requires that some unlocking means by applied from the surface in order to break this hydraulic lock. Conventionally, a ball or dart or the like is dropped down the interior of the drill stem from the surface in order to attempt to open the valve, but this practice is generally unpredictable and unsatisfactory.